A liquid crystal display device which controls alignment of a liquid crystal to perform display has advantages such as slim profile, lightweight, and low power consumption, in comparison to CRT that is a conventional standard display. Therefore, such a liquid crystal display device has been widely used in various electronics. Particularly in an application such as a household TV, use of such a liquid crystal display device has been rapidly increased, recently. Various studies on a method of controlling alignment of a liquid crystal have been made in order to improve display qualities of this liquid crystal display device.
Multi-domain Vertical Alignment (hereinafter, also referred to as MVA) mode is known as a display mode effective for widening a viewing angle and improving a contrast ratio. FIG. 1 shows a configuration of a liquid crystal display device in MVA mode (MVA-LCD). As shown in FIG. 1, according to the MVA-LCD, liquid crystals 12 are aligned in accordance with a plurality of domains using a projective structure 13 formed on a substrate or a slit 11a provided for an electrode 11 for liquid crystal driving, formed on the substrate, in Vertical Alignment mode where the liquid crystals 12 are aligned to be substantially vertical to the electrode 11 during no voltage application and the liquid crystals 12 are aligned to be substantially parallel to the electrode 11 during voltage application.
The MVA-LCD can effectively widen the viewing angle and improve the contrast ratio, but it has still room for improvement in response speed. Particularly, an improvement in response speed at the time of intermediate scale display is needed for the MVA-LCD. Only liquid crystal molecules near the projective structure and/or the electrode slit can be quickly aligned in response to a voltage applied to the liquid crystal. Liquid crystals far from these alignment control structures respond late. Due to the low response speed of the liquid crystal, blurred moving images might be displayed. The MVA-LCD has also room for improvement in that the projective structures and/or the electrode slits reduce an aperture ratio (transmittance).
A Polymer Sustained Alignment (hereinafter, also referred to as PSA) technology has been known as a technology for improving the response speed or the aperture ratio (for example, refer to Patent Documents 1 to 3). FIG. 2 shows a schematic view showing the Polymer Sustained Alignment (PSA) technology. FIG. 2(a) shows a state where light is radiated for forming a polymer. FIG. 2(b) shows a liquid crystal display panel where a polymer has been formed by the photopolymerization. As shown in FIG. 2, according to the PSA technology, a monomer 14 is dispersed into liquid crystal 12, and under voltage application to the liquid crystal 12, the monomer 14 which has been dispersed into the liquid crystal 12 is photopolymerized by irradiation of light 16, thereby forming a polymer 14a on a surface of an alignment film 15. Then, this polymer 14a determines a pretilt of the liquid crystal 12 which is positioned on the surface of the alignment film 15.
According to the MVA-LCD, the alignment control is performed using only the projective structures and/or the electrode slits. Therefore, liquid crystal molecules near the projective structure and/or the electrode slit start to respond, followed by liquid crystal molecules at the intermediate part. In contrast, in a liquid crystal display device to which the PSA technology has been applied (PSA-LCD), polymers formed on the alignment film surface perform alignment control, and therefore, liquid crystal molecules in a region where the polymers have been formed respond at the same time. In the case that the PSA technology is applied to the MVA-LCD, the alignment control attributed to the MVA-LCD itself and the PSA technology is performed. The liquid crystal molecules near the projective structure and/or the electrode slit respond first, but shortly after that, the liquid crystal molecules at the intermediate part also respond at the same time. In addition, the PSA-LCD is advantageous in terms of aperture ratio (transmittance) because occupancy of the projective structure and/or the electrode slit on the substrate surface can be reduced or eliminated.
However, the PSA-LCD also has room for improvement in alignment stability of liquid crystal and improvement in response speed of liquid crystal.    [Patent Document 1]    Japanese Patent No. 3520376    [Patent Document 2]    Japanese Kokai Publication No. Hei-08-114804    [Patent Document 3]    Japanese Kokai Publication No. 2003-177418